The present invention relates to a fluorescent lamp including two electrodes and 2n glass tubes, where n is at least 2. the tubes being connected by respective bridge parts to form a discharge path through the tubes between the two electrodes. The invention further relates to a method for manufacturing such a fluorescent lamp.
A method for manufacturing a fluorescent lamp with eight tubes is described in UK Patent Application GB 2 335 538. The lamp is assembled from four dual tubes that are previously manufactured. Dual tubes are manufactured from two parallel glass tubes each having one end sealed. The tubes are connected to each other by means of a bridge near the sealed tube ends. The distance created between the bridge and the sealed tube ends is of such a dimension that a cold spot is created in both tube end parts. These cold spots are intended for mercury vapor pressure control and, as mercury vapor pressure determines the lamp lumen output, the effectiveness of the lamp. In the finished lamp the number of cold spots equals the number of tubes, e.g. in the lamp according to GB 2 335 538 there are eight cold spots. The creation of more cold spots than one being needed for mercury vapor pressure control is at the expense of light-emitting tube area, resulting in a lower luminous flux or longer lamp length.
The object of the invention is to provide an improved fluorescent lamp for which above-mentioned drawback does not arise.
This object is achieved in accordance with the invention with a fluorescent lamp defined in the introduction which is characterized in that the first bridge part of the first dual shaped lamp part is located at a distance d1 from the sealed ends of the tubes, and that the second bridge part of the second dual shaped lamp part is located at a distance d2 from the sealed ends of the tubes, wherein the distance d2 is shorter than the distance d1 such that only a cold spot is formed in a tube end part of the first dual shaped lamp part. Only one dual shaped lamp part has a cold spot, while the or each other dual shaped lamp part fully utilizes its length for the gas discharge, light-emitting area, which will result in a higher lumen output or reduced total lamp length.
The invention also relates to a method for manufacturing a fluorescent lamp as defined in claim 2.